SIM identifiers ICCID, IMSI, IMEI, EID and MSISDN

A cellular device carries several numbers that look alike. They identify different things, and they change at different times. Knowing which is which saves confusion when you order SIMs, track devices or talk to support.

The five numbers

• ICCID is the SIM’s serial number. It is printed on a SIM card and stored inside it. On an eSIM there is one ICCID for each operator profile. It starts with 89, the code reserved for telecommunications.
• IMSI identifies the subscription to the mobile network. The network uses it to recognise the SIM and authenticate it. Its first three digits are the country code, such as 234 or 235 for the UK, and the next two or three identify the home network.
• IMEI identifies the device, or more precisely its cellular module. It is 15 digits and belongs to the hardware, whatever SIM is fitted.
• EID identifies an eUICC, the kind of SIM chip that can hold several profiles and download new ones. It is 32 digits and stays with the chip for its life.
• MSISDN is the phone number. It is needed for calls and for SMS to and from ordinary phone numbers. A data-only subscription may not have one.

Who owns what

Three things are being identified.

• The device has the IMEI.
• The SIM chip has the EID if it is an eUICC. An ordinary SIM card is identified by its ICCID.
• The subscription has the IMSI and the MSISDN, and on an eSIM the profile also has its own ICCID.

What changes when

If you put a different SIM card in a device, the ICCID, IMSI and usually the phone number change. The IMEI stays the same.

If an eUICC switches to another profile, the ICCID, IMSI and usually the phone number change. The EID and IMEI stay the same.

If you replace the device or its module, the IMEI changes. With a removable SIM that moves across, the SIM’s numbers stay the same. If the SIM is soldered to the board being replaced, its numbers change too.

Why it matters

Use the right number for the job. Order, activate and bill SIMs by ICCID. Track hardware by IMEI. Identify an eUICC by EID when loading profiles. Record all of them when each device is built, so you can match a SIM to a device later.

ICCID

The Integrated Circuit Card Identifier is a primary account number under ITU-T E.118. It is made up of

• the issuer identification number, which is the Major Industry Identifier 89 (assigned to telecommunications under ISO/IEC 7812-1), an E.164 country code of 1 to 3 digits and an issuer identifier, at most 7 digits in all;
• an individual account number;
• a check digit calculated with the Luhn formula.

E.118 has set a maximum of 19 digits, check digit included, since its 2006 edition, and the 2025 edition requires new numbers to be exactly 19 digits. Numbers already issued are not affected. The card stores the ICCID in EF ICCID (‘2FE2’, ETSI TS 102 221 clause 13.2), a 10-byte BCD file padded with ‘F’, which has room for 20 digits. Store ICCIDs as text of up to 20 digits.

On a removable SIM the ICCID is printed on the card and the same value is stored in it. On an eUICC each profile has its own ICCID. The chip itself is identified by the EID.

IMSI

The International Mobile Subscription Identity identifies the subscription to the network. 3GPP TS 23.003 clause 2.2, which follows ITU-T E.212, sets its structure at not more than 15 digits:

• MCC, the Mobile Country Code, 3 digits;
• MNC, the Mobile Network Code, 2 or 3 digits, the length depending on the MCC;
• MSIN, the subscriber number within that network.

MCC plus MNC identifies the home network (the home PLMN). The UK uses MCCs 234 and 235, and networks in the Channel Islands and the Isle of Man hold codes under 234 in the ITU’s list. The IMSI is stored in the USIM and used by the network to find the subscription and authenticate it. To protect privacy the network gives the device temporary identities, such as the GUTI in LTE, and these are used over the air in its place where possible.

A subscription can change IMSI while keeping its phone number (TS 23.003 clause 3.2). A multi-IMSI SIM uses this. It switches between IMSIs from different home networks while its ICCID stays the same.

IMEI and IMEISV

The International Mobile Equipment Identity identifies the mobile equipment, which in an IoT product is the cellular module. TS 23.003 clause 6.2 defines

• IMEI, 15 digits. An 8-digit Type Allocation Code (TAC), issued by the GSMA, a 6-digit serial number and a check digit calculated with the Luhn formula. The check digit is for manual entry and is sent as 0 over the network.
• IMEISV, 16 digits. The same TAC and serial number followed by a 2-digit software version number, with no check digit.

EID

The eUICC Identifier identifies an eUICC chip. GSMA SGP.22 section 4.3.1 and SGP.29 define it as 32 digits: an EUM Identification Number of the manufacturer, a manufacturer-specific number and two check digits. The check digits are calculated over all 32 digits with a modulo 97 method. An EID is valid when the 32-digit number divided by 97 leaves a remainder of 1.

There are two assignment schemes. The original one, first defined in SGP.02, follows E.118, so those EIDs start with 89 followed by a country code. Under SGP.29 the GSMA assigns number ranges itself, and those EIDs never start with 89. Both remain valid. SGP.29 states that the EID is not related to subscriptions and cannot be used to identify them. The device’s local profile assistant reads it from the eUICC, and remote provisioning uses it to identify the target chip.

MSISDN

The MSISDN is the subscription’s international phone number, an ITU-T E.164 number of at most 15 digits. It is a country code of 1 to 3 digits followed by a national destination code and subscriber number (TS 23.003 clause 3.3). It is held in the home network’s subscriber records and maps to the IMSI there.

TS 23.003 clause 3.1 makes an MSISDN mandatory in general but allows GPRS and EPS subscriptions without one. Where a message still needs the field, a dummy value of fifteen zeros is used. A data-only IoT subscription can therefore work without one, though voice and SMS to ordinary phone numbers need it.

Which identifier belongs where

Practical points for IoT

• Record the IMEI, ICCID and, for an eUICC, the EID of every unit at production, together with the device serial number. With a soldered SIM or an eUICC this pairing is the only reliable way to match a device to its connectivity later.
• Read the identifiers from the module rather than from labels. 3GPP TS 27.007 defines AT+CGSN for the IMEI and AT+CIMI for the IMSI, and the ICCID can be read from EF ICCID with the restricted SIM access command AT+CRSM. AT+CRSM returns it with F padding, and usually with each pair of digits swapped.
• Validate before storing. Luhn for ICCID and IMEI, modulo 97 for EID.
• The IMSI identifies a subscriber. Where a device belongs to a person, treat it as personal data and keep it out of URLs and shared logs.

See also network selection, SIM form factors and eSIM, eUICC and MFF2.